-- Adds the most-recent-purchase supplier/date to feed_stock, kept in sync by
-- purchase() on every new delivery (same rolling treatment as unit_cost) and
-- still directly correctable via a plain edit, same as qty/cost/reorder. The
-- full, immutable history of every individual delivery still lives in
-- feed_purchases — this is just "who/when for the current pile," surfaced on
-- the Unmixed feed inventory table.
ALTER TABLE feed_stock
  ADD COLUMN supplier     VARCHAR(160) NULL AFTER unit_cost,
  ADD COLUMN purchased_on DATE         NULL AFTER supplier;